Why cant other space craft go that fast?

[spurius]

http://en.wikipedia.org/wiki/Helios_2_(NASA)

157000mph is blumming fast. over 3 times faster than new horizons was at jupiter, but the suns gravity has apparently slowed that down further. So why cant spacecraft sent to the outer solar system achieve these kinds of speeds? Its obviously possible.

Im assuming it has something to do with the need to slow the spacecraft down when it reaches its destination.

[sgazer]

The speed isn't really reached due to the on board propulsion, it's more due to the gravity of the object it's heading towards. They don't have enough fuel and power after taking off from earth for a sustained boost in speed. Going towards the sun is going to accelerate things significantly due to it's immense gravity (it's holding the earth in orbit at this distance despite us travelling at 67,000mph). The object arriving at the sun would need to have high speed to stay in orbit, otherwise it would plummet towards the sun.

Objects travelling out of the system are typically accelerated with a loop around the sun, but as they travel away, they are slowed by its pull backwards, but they also use other planets like Jupiter and Saturn to give them a boost.

[gkec]

sgazer is right in that it is mainly orbital velocity. Mercury orbits at a maximum of 59km/sec so 70km/sec seems reasonable as the fastest point of Helios's orbit would be at perihelion which is within the orbit of Mercury.

Aphelion is very near Earth orbit so it probably didn't take much fuel to alter the orbit for it to fall towards the Sun.

[spurius]

The speed isn't really reached due to the on board propulsion, it's more due to the gravity of the object it's heading towards. They don't have enough fuel and power after taking off from earth for a sustained boost in speed. Going towards the sun is going to accelerate things significantly due to it's immense gravity (it's holding the earth in orbit at this distance despite us travelling at 67,000mph). The object arriving at the sun would need to have high speed to stay in orbit, otherwise it would plummet towards the sun.

Objects travelling out of the system are typically accelerated with a loop around the sun, but as they travel away, they are slowed by its pull backwards, but they also use other planets like Jupiter and Saturn to give them a boost.

Thats cheatin! I came across that article when searching for the fastest ever man made object. Off to find the fastest man made object under its own power.

[Naemeth]

Thats cheatin! I came across that article when searching for the fastest ever man made object. Off to find the fastest man made object under its own power.

Spacecraft probably... the escape velocity of the Earth is about 11 km/s (11.2 km/s). No, I'm not converting to miles per hour .

[sgazer]

if you class a photon as an object, then as 'man' makes light, I guess that's the fastest man-made object LOL

[Iddy]

OK here's a mind bender for you :

Since Nasa is now working on its own Alcubierre Drive ( yes i know, far far away, but lets assume they manage to get it working) would this consist the fastest man made object? Since technically it works on bending space and time, and the craft is in essence standing still... its just the universe that flowing around it really really mindboggeling fast.....

( yes I have to much free time to think about stuff like this )

[Knight of Clear Skies]

Thats cheatin! I came across that article when searching for the fastest ever man made object. Off to find the fastest man made object under its own power.

Funnily enough, I was reading about this just today; there is one other candidate which isn't a space probe. There was an incident during one early nuclear test where a 4 foot steel plate was expelled upwards, like a fission-powered potato cannon. It's actual speed was never established, but the minimum value was 66 km/s. This is more than five times escape velocity. However, the plate wouldn't have made it into space, as it would have been stopped or destroyed by contact with the atmosphere.

[michael.h.f.wilkinson]

Spacecraft probably... the escape velocity of the Earth is about 11 km/s (11.2 km/s). No, I'm not converting to miles per hour .

I do not know about mph but it is about 67,344,309 furlongs per fortnight

[Knight of Clear Skies]

I do not know about mph but it is about 67,344,309 furlongs per fortnight

Don't know about you, but I'd bet on that horse.

[spurius]

OK here's a mind bender for you :

Since Nasa is now working on its own Alcubierre Drive ( yes i know, far far away, but lets assume they manage to get it working) would this consist the fastest man made object? Since technically it works on bending space and time, and the craft is in essence standing still... its just the universe that flowing around it really really mindboggeling fast.....

( yes I have to much free time to think about stuff like this )

What do you mean "bending space and time"? I can for example bend a piece of plastic. With enough force I can even bend metal. One example would be to insert a long piece of thin metal into a vice and pull or push on the other end. But in what way could you apply force to something like physical nothingness or even air? I could swing a baseball bat at air but the bat would just travel though it. Swinging it fast enough may cause a shockwave or something but you wouldnt even get that in space. Explain.

[spurius]

Spacecraft probably... the escape velocity of the Earth is about 11 km/s (11.2 km/s). No, I'm not converting to miles per hour .

Heres another one for you. What happens if you point a rocket bang on in the direction of M31 but only used enough force to travel a constant 9km/s? Or is the escape velocity referring to what a bullet would need to be travelling at when it left the gun to get into space?

[Naemeth]

Heres another one for you. What happens if you point a rocket bang on in the direction of M31 but only used enough force to travel a constant 9km/s? Or is the escape velocity referring to what a bullet would need to be travelling at when it left the gun to get into space?

It's the minimum velocity needed to escape Earth's gravity, in this case, you wouldn't leave the Earth - Moon system .

http://en.wikipedia.org/wiki/Escape_velocity

[Iddy]

What do you mean "bending space and time"? I can for example bend a piece of plastic. With enough force I can even bend metal. One example would be to insert a long piece of thin metal into a vice and pull or push on the other end. But in what way could you apply force to something like physical nothingness or even air? I could swing a baseball bat at air but the bat would just travel though it. Swinging it fast enough may cause a shockwave or something but you wouldnt even get that in space. Explain.

Ok stolen this from the internet, since i'm to lazy today to type it out

How the Alcubierre Drive Works

Normally, Einstein's theory of relativity doesn't permit any object to travel faster than the speed of light, because accelerating up to that speed requires an infinite amount of energy. The Alcubierre drive gets around this by proposing that the drive would actually manipulate spacetime itself, causing the space in front of it to contract while the space behind it expands. This "warp bubble" allows the ship to reach a destination faster than a light beam traveling through "normal" spacetime.

According to relativity, space is malleable, which is how the Alcubierre drive achieves this feat. (The early universe, for example, expanded faster than the speed of light because spacetime itself can expand faster, even though objects within spacetime cannot accelerate faster.) In this scenario, the ship containing the Alcubierre drive actually sits still and is carried along the warp bubble, kind of like a surfboard riding on an expanding wave. This means that time dilation and other relativistic effects aren't significant, despite the intense speed.

See it like you're want to go somewhere, so everything around you moves beneath you, but you are in the same location. So you're standing still, the rest of the universe just moves. Its the scientific principle behind the " warp drive" from star trek.

[J_M_Franklin]

http://en.wikipedia..../Helios_2_(NASA)

157000mph is blumming fast. over 3 times faster than new horizons was at jupiter, but the suns gravity has apparently slowed that down further. So why cant spacecraft sent to the outer solar system achieve these kinds of speeds? Its obviously possible.

Im assuming it has something to do with the need to slow the spacecraft down when it reaches its destination.

The biggest constraint on the speed of a space vehicle to date is the use of chemical rockets and the fact that because they need to be launched with their fuel there is a limit to how much they are able to carry, thus this limits their forward thrust because once it is depleted (the fuel) they simply coast at the final velocity they had when they ran out of fuel.

Ion drives (Electric propulsion systems) change all this, and although NASA has been experimenting since 1964 so far only a couple of craft have used the technology, and only one for main propulsion. At the moment Ion drives cannot compete head to head with chemical engines, but they are able to thrust for longer, much longer in fact, a chemical rocket may have enough fuel for perhaps a 60 minute burn at best, but Ion drives can continue to operate for thousands of hours so they can end up with higher forward velocities as a result. The gravity of a body is totally irrelevant to any of this. The gravity only comes into it if you do not want your craft/vehicle captured or otherwise negatively impacted by the gravity well of the object your approaching.

[Jessun]

On a side note, Michio Kaku wrote in one of his books that in order to reach our nearest star beyond the Sun, using conventional liquid fuel rockets and completing the journey in 100 years, the fuel tank would have to be five times larger than the size of the observable Universe. Cost would hinder this approach.

/Jesper

[J_M_Franklin]

On a side note, Michio Kaku wrote in one of his books that in order to reach our nearest star beyond the Sun, using conventional liquid fuel rockets and completing the journey in 100 years, the fuel tank would have to be five times larger than the size of the observable Universe. Cost would hinder this approach.

/Jesper

That can't be right as the maths don't stack up. To reach Alpha Cen A/B in 100 years would mean travelling at 23.25581% light speed, or 69719.19581 km/s^-1 which is 250,989,104.9 km/hr.

Now if you accelerated at a constant rate of 1G or 9.8m/s^-1 then in 1 hour you would be travelling at 35,280 m/s^-1 and it would take a little over 1,976,162 hours (82,340 days / 225.5 years) to reach the required velocity of 69719km/s^-1.

Clearly 1G acceleration would not be achievable, thus to achieve what you want you would actually have to accelerate to a velocity of 157,147.0674 km/s-1 or 565,719,442.5 km/hr.

The acceleration would also have to be twice this because you could only accelerate half way if you wanted any hope of stopping there, so you would need half the distance to stop...

All the chemicals in the Universe would not make it achievable..

[Jessun]

All the chemicals in the Universe would not make it achievable..

Precisely. The size of the tank is 5 times bigger than the observable Universe. I trust that the professor has done his maths! I'm clueless btw, so can't really argue either... But why would 1g not be achievable? Rockets reach 5 to 7g - and that's fairly close to Earth, so way out there, I'm sure you can accelerate a lot more?

/Jesper

[Naemeth]

Someone needs to make a "Dark Energy" warp drive .

[J_M_Franklin]

Precisely. The size of the tank is 5 times bigger than the observable Universe. I trust that the professor has done his maths! I'm clueless btw, so can't really argue either... But why would 1g not be achievable? Rockets reach 5 to 7g - and that's fairly close to Earth, so way out there, I'm sure you can accelerate a lot more?

/Jesper

Jesper, it's the time issue that makes Chemical rockets wrong for it. Chemical rockets could not thrust a vehicle continually fast enough to achieve the aimed time frame, even if you had enough Chemicals. Chemical rockets have an upper limit to their thrust capabilities which means that sustaining anything more than 3 G is impractical, and above 3G the impact on people would be rather unpleasant (not that 3G is "nice")

To reach A Cen A/B in 100 years is achievable with ion drives because they are not limited like chemical rockets, you can get a lot of thrust from a small amount of fuel. At the moment we have only scratched the surface of what we can engineer, but mathematically speaking an Ion drive can be made to accelerate in a logarithmic way so that you start at 1G but this creeps up over time so there is no noticeable acceleration on the occupants, the change can be accounted for by the body and inertial dampers. Realistically it is mathematically to achieve accelerations of up to 100G with no impact on the human body (The engineering is the restricting factor here and not the science). The 100G could be achieved within 10 months of the journey start and that gives a forward velocity of 980m/s^-1, which is still only 3,528 km/hr.

In order to achieve a realistic speed across the gulf of space you need to have a forward velocity of at least 1 Mega G or 9.8⁶m/s^-1 which is 35.280⁶km/hr it would still take more than 7 years to reach A Cen A/B, and that is assuming you want a flyby and not stop!!

[Jessun]

The 100G could be achieved within 10 months of the journey start and that gives a forward velocity of 980m/s^-1, which is still only 3,528 km/hr.

Are you suggesting that a 100G acceleration over 10 months will only reach this speed? Heck I've flown 2000 km/hr in a simple aeroplane!! Took me about 40 seconds to reach Mach 2....

Weight is the issue with liquid fuel rockets, and nothing else. Put more fuel in and you need more thrust to accelerate that fuel. So you need more fuel. Etc, etc. Actual output in pounds of thrust is totally unlimited - if you think a particular engine is at its limit, put 1000 more on the ship, or a billion. That's the point Kaku makes. The weight of the fuel is the only issue, to complete trip in that time frame. (I can't remember if he argued that a person would survive the trip G-wise).

Speaking of which, lying down in an experimental water filled G-suit, test pilots can pull 12G for a good few seconds in centifuge runs. I've only done 9 myself, small blood vessels already rupture at 9G, and the blood runs backwards in the veins - this is particularly painful. Your heart actually stops, and you breathe in short bursts every three seconds, not to give you oxygene - anyone can hold their breath for a minute, but the movement of your lunges effectively gives the heart CPR, since having the shape of a banana, it can't beat. 100G sounds totally unachievable to me.

/Jesper

[J_M_Franklin]

Are you suggesting that a 100G acceleration over 10 months will only reach this speed? Heck I've flown 2000 km/hr in a simple aeroplane!! Took me about 40 seconds to reach Mach 2....

Weight is the issue with liquid fuel rockets, and nothing else. Put more fuel in and you need more thrust to accelerate that fuel. So you need more fuel. Etc, etc. Actual output in pounds of thrust is totally unlimited - if you think a particular engine is at its limit, put 1000 more on the ship, or a billion. That's the point Kaku makes. The weight of the fuel is the only issue, to complete trip in that time frame. (I can't remember if he argued that a person would survive the trip G-wise).

Speaking of which, lying down in an experimental water filled G-suit, test pilots can pull 12G for a good few seconds in centifuge runs. I've only done 9 myself, small blood vessels already rupture at 9G, and the blood runs backwards in the veins - this is particularly painful. Your heart actually stops, and you breathe in short bursts every three seconds, not to give you oxygene - anyone can hold their breath for a minute, but the movement of your lunges effectively gives the heart CPR, since having the shape of a banana, it can't beat. 100G sounds totally unachievable to me.

/Jesper

Jesper, there are physical limits to what Chemical rockets are able to achieve, no matter how many rockets you add to a vehicle, We are not there yet, the maximum thrust achievable equates to about 25G acceleration (that is not actually 25G) and this is because the laws of physics imposes limits on the output and as you state, there is a trade off between the amount of fuel you can realistically carry before your simply wasting fuel moving fuel. Saturn 5 rockets actually used nearly 30% of their fuel up just moving the fuel load of the rocket and something in the region of 60% of their thrust was required to achieve this.

If a Saturn 5 was built and launched in Orbit the results would be a lot different, it's forward speed would be in the region of 45,000km/hr, however due to the rapid acceleration the people on the vehicle would experience a massive G loading and thus this is another limiting factor for manned chemical rockets, realistically they cannot accelerate at more than 2.5G before this forward motion becomes uncomfortable for the occupants.

What this means is that with our current technology (inertial dampers) we are limited in the acceleration to something that builds up over time. Electric propulsion systems offer this ability to achieve massive forward velocity over extended periods of time that are simply not achievable with chemical systems.

By the way, in speaking about the forward velocity of a vehicle in space it is normal to speak of this in terms of G and this does not mean the true acceleration is 100G in a short time, no human could withstand a true acceleration (as we think of it on Earth) of more than 25 G (Horizontal axis G force) as this would cause massive internal damage to blood vessels, eyes, brain matter and internal organs. This is far higher than standard vertical axis G-Force (which Pilots experience) and has a normal limit of around 5 G and trained pilots about 9 G.

In future, to avoid confusion i will refer to forward velocity only in km/hr.

[Jessun]

A simple chemical ASRAAM accelerates at 60+G at sealevel. Maybe fireworks rockets launch with even greater G-load - I don't know.

What is this limit you mention? It all depends on what output/versus accelerated mass you have - and ultimately what you want to achieve. It would be pointless to launch astronauts at 60G, but totally possible.

When you mean that Ion drives build up acceleration over time, I don't quite follow. Acceleration doesn't necessarily build up at all - it's the speed that builds up. Ion engines have the advantage to use very little fuel, so they can run for very, very long time - gradually building up great speed. The G force remains the same throughout until Einsteins equations kick in at very high speeds.

By the way, in speaking about the forward velocity of a vehicle in space it is normal to speak of this in terms of G and this does not mean the true acceleration is 100G

It's only fair to say that I don't normally speak about these matters - I'm not educated enough , so I don't understand this one, but happy to listen.

/Jesper

[spurius]

Ok stolen this from the internet, since i'm to lazy today to type it out

How the Alcubierre Drive Works

Normally, Einstein's theory of relativity doesn't permit any object to travel faster than the speed of light, because accelerating up to that speed requires an infinite amount of energy. The Alcubierre drive gets around this by proposing that the drive would actually manipulate spacetime itself, causing the space in front of it to contract while the space behind it expands. This "warp bubble" allows the ship to reach a destination faster than a light beam traveling through "normal" spacetime.

According to relativity, space is malleable, which is how the Alcubierre drive achieves this feat. (The early universe, for example, expanded faster than the speed of light because spacetime itself can expand faster, even though objects within spacetime cannot accelerate faster.) In this scenario, the ship containing the Alcubierre drive actually sits still and is carried along the warp bubble, kind of like a surfboard riding on an expanding wave. This means that time dilation and other relativistic effects aren't significant, despite the intense speed.

See it like you're want to go somewhere, so everything around you moves beneath you, but you are in the same location. So you're standing still, the rest of the universe just moves. Its the scientific principle behind the " warp drive" from star trek.

Sounds like something taken out of futurama lol! But I do see a problem with this theory. If you were to get somewhere by moving the universe around you then thats fine. The problem would be if someone else tried the same thing at the same time. It would literally ruin a perfectly good universe.

[J_M_Franklin]

A simple chemical ASRAAM accelerates at 60+G at sealevel. Maybe fireworks rockets launch with even greater G-load - I don't know.

Last time I looked the ASRAAM was pilotless so the acceleration is meaningless to this discussion, the fuel it has gives it something like 2 minutes of burn and then it is out of fuel, so not a great example..

What is this limit you mention? It all depends on what output/versus accelerated mass you have - and ultimately what you want to achieve. It would be pointless to launch astronauts at 60G, but totally possible.

The limit is set by the true force exerted on a human body and the amount of fuel the vehicle can economically carry, however there is a maximum output for a chemical rocket and from memory that is somewhere in the region of 90G

When you mean that Ion drives build up acceleration over time, I don't quite follow. Acceleration doesn't necessarily build up at all - it's the speed that builds up. Ion engines have the advantage to use very little fuel, so they can run for very, very long time - gradually building up great speed. The G force remains the same throughout until Einsteins equations kick in at very high speeds.

The acceleration can be controlled with an Ion drive so the acceleration can be increased over time to the level desired without the punch in the gut you get from chemical rockets. The G force exerted is a product of the acceleration so it only remains constant if the acceleration remains constant. If the drive is powered up to 1G acceleration and this is then increased slowly the forward velocity increases but the increase is at a level that become almost imperceptible to the occupants. It is difficult to control these drives to the level of precision required for human occupants, this is part of the reason why they have not advanced as far as we would all like, but technology moves on and it's only a matter of time before this nut is cracked.

It's only fair to say that I don't normally speak about these matters - I'm not educated enough , so I don't understand this one, but happy to listen.

/Jesper

Jesper, that is why i said from now on I will do velocities in km/s or km/hr to keep it simple